Sometimes RFI problems are self-inflicted.
Eric Berger in Florida recounts that several
years ago a friend who works in aviation dropped by for a casual visit. He
wanted to listen in on the aircraft band. Eric’s ham radio had a VHF general
coverage receiver, so they started tuning around.
Fig. 1: Try your cell camera if you need to read a serial number that’s
on the side of rack-mounted equipment.This isn’t a great photo, but it did the job in a tight place. The
important thing is that we can make out the number.
When they heard a strong but garbled wideband signal, they switched from
AM to FM and heard a local FM station in the VHF aircraft band. A little
checking revealed several FM translators colocated a few miles from Eric’s
house. The sum of two of the frequencies minus another fell right on the
Eric reported this intermod problem to
the “station engineer,” who was polite but dismissive.
After days of inaction turned into
weeks, our heroes notified the FCC and FAA. Problem solved. The station
engineer had been given a chance to resolve this discreetly but chose instead
to make a federal case out of it. Denial is not a solution to RFI problems.
Eric, your situation brings to mind a
similar one in a major market in which an engineer uncovered spurs, but the manager
turned a deaf ear because it was the middle of a ratings period. When the
inspector showed up, this GM remained defiant, saying the man from the
commission had no authority to take the station off the air. The manager’s jaw
hit the floor when the inspector did just that.
In an era without FCC operator
licensing, at a time when many staff scoff at FCC rules, public safety and
interference issues are not to be taken lightly. Instruct your receptionist and
air staff to report any complaints to you immediately.
Eric Berger has spent most of his career
in RF and microwave engineering, and has resolved quite a few RFI and intermod
* * *
From the blog at www.theonlineengineer.org comes word of “The Switch.”
Fig. 2: The Switch provides customer-controlled
video switching services. It is owned by Beers Enterprises Inc.
The Switch is a company that has been
getting fiber optic lines from AT&T and leasing them for less to
broadcasters and others around the U.S. as well as outside the country. They apparently
want your business in uncompressed 3G, HD-SDI, SD-SDI and ASI transport.
These standards typically are used for
transmission of uncompressed, unencrypted digital video signals, but can
include embedded audio and/or time code. The transports also can be used for
packetized data. Folks from The Switch approached the blogger as chief of his
station and offered a fiber optic circuit STL for a few hundred less than what it
was paying AT&T.
Saving money is always good. You can
find more information at www.theswitch.tv.
* * *
Here’s a tip from prolific RW contributor
Buc Fitch, P.E.
The National Electric Code, in section
230.28 of the 2005 edition (which is used in Connecticut), prohibits using an
electric service mast to mount FM or TV antennas. This prohibition appears in
all ensuing editions of the code as well.
The regulation essentially says that
the electric service mast is exclusively and only for the support of the
electric service. The most usual violation of this regulation is the use of the
mast to support telephone cables! Resist the temptation.
Buc, our favorite repair guy, is
rescuing a Harris MS-15 exciter. He writes that he’s not out of the woods yet;
after repairing all the power supply damage, he discovered that the RF module
has a defective AGC switch, a butchered power adjust pot and a dim 15 volt
present LED. What cowboy worked on this thing?
Buc says he’ll bring it back to life, because
these exciters can run on and on if the fan moves enough air through the box
and the heat sinks.
One helpful change was to remove the
shield (fan guard) in the air path between the bottom of the fan in the PS
cavity and the card cage below. Buc writes that this is a part either included
by an ultra-conservative safety engineer or dictated by a lawyer (finger risk
After his mod, the air flow picked up
* * *
Ron Foo was with Clear Channel San
Diego for 21 years. He writes that he used to buy most of his hardware, and
still does, from McMaster-Carr.
They have several warehouses in the United States, with an excellent selection
of hardware in various materials, e.g., stainless steel, brass, nylon and steel.
There’s no minimum order, and they
probably have what you are looking for. The company also stocks all sorts of
odd pieces of hardware that today’s broadcast engineer is seeking. Rather than
guess about what big-box hardware stores will have in stock, try the McMaster
A wonderful source of tools and materials
is MSC. They have
hard-to-find machine tools, cutters and drill bits. Their selection includes left-handed
drill bits for removing broken screws and bolts (though noleft-handed
Ron Foo now works as an R&D engineering
technician for Seek Tech Inc. in San Diego. The company makes underground
utility locating equipment and pipe inspection equipment.
* * *
Entravision’s Robert Smith recently expressed
his frustration toward equipment design engineers who decide to place serial
number information on the sides of
Not a good idea. Most racks offer
little light. And even if you can get your eyes in the cramped space, few
engineers are adept at reading sideways.
But Robert writes that sometimes you
can get lucky. In this case, he could squeeze his hand inside the rack and use
his Droid cell phone camera to take a picture of the identification plate. This
is one reason the cellphone or digital camera ranks number one as the most
valuable tool for engineers.
Digital shots also can identify
unlabeled parts and assist with troubleshooting when talking to a service
Contribute to Workbench. You’ll help your fellow engineers and qualify
for SBE recertification credit. Send Workbench tips to firstname.lastname@example.org. Fax
to (603) 472-4944.
John Bisset has spent 43 years in the broadcasting industry and is still
learning. He is SBE Certified and is a past recipient of the SBE’s Educator of
the Year Award.